1. Field of the Invention
The present invention relates to a current sensor and a method of manufacturing the current sensor.
To be specific, the present invention relates to a current sensor of magnetoelectric conversion type, which measures the intensity of a current by detecting a flux generated by the current to be measured with a magnetic field detection element, and a manufacturing method thereof.
2. Description of the Related Art
A Hall sensor using the Hall effect, a magnetoresistive element, a magnetic transistor, etc (or these including an ASIC for amplifying function or adjusting function) are widely known as magnetic sensors. Capturing a magnetic flux created around a current to be measured and measuring its current intensity can be done by using such magnetic field sensors.
For this purpose, a current sensor structure shown in FIG. 1 is widely used conventionally.
However, the current sensor having the configuration of FIG. 1 is not suitable for miniaturization because the sensor requires a magnetic core 4 surrounding a current conductor 2 fed with current. Further, since the magnetic core 4 and a Hall element 6 need to be separately manufactured and then assembled into one, the sensor has not been suitable for mass production and the cost is not low.
In order to solve such an inconvenience, “a magnetic field sensor with a terminal for detecting current” containing a chip with a magnetoelectric conversion element sealed with plastics has been proposed in Japanese Patent Application Laid-Open No. 61-80074 (1986). This publication discloses “a magnetic field sensor with a terminal for detecting current. This magnetic field sensor comprises a current conductor, a magnetoelectric conversion element chip placed on a part of the above current conductor (except both sides of the conductor), lead frames (each side of which are connected to the chip) and a sealing part (for integrally sealing the end of the lead frame, the magnetoelectric conversion element chip, and the part of the chip located on a current conductor). This magnetic field sensor is characterized in that the sensor has both ends of the current conductor as external terminals for current detection”.
However, the invention disclosed in Japanese Patent Application Laid-Open No. 61-80074 (1986) has the following problems:
In the invention disclosed in Japanese Patent Application Laid-Open No. 61-80074 (1986), when current flows in the current conductor, a flux appearing concentrically around the current conductor is detected by a magnetic field sensor chip which is placed closely to a surface of the current conductor. And the magnetic field sensor chip mainly has sensitivity only to a flux which is perpendicular to the surface of the chip. The sensor has extremely low sensitivity to a flux in a horizontal direction. For this reason, it is difficult to detect current with high sensitivity.
The magnetic field sensor chip is sensitive to a flux which is perpendicular to the surface of the chip. It is rotated by 90°, and further, the magnetic field sensor chip is placed on a current conductor to detect the current flux in such a way that a flux generated by the current goes through the chip surface perpendicularly.
However, the invention is not practical and lacks mass productivity, considering complexity of a method of fixing the magnetic field sensor chip on the current conductor and a wire bonding method between a sensor chip terminal and a lead frame.
(2) There may be a current which is not a current to be measured around the current sensor. In such an environment, the invention disclosed in Japanese Patent Application Laid-Open No. 61-80074 (1986) is susceptible to an external flux generated by surrounding current. Thus, it is difficult to detect accurately a flux generated by the current to be measured.
(3) In the invention disclosed in Japanese Patent Application Laid-Open No. 61-80074 (1986), the current conductor and the surface of the lead frame (which is connected to the terminal of the magnetic field sensor chip) are not formed on the same height of a plane. Thus, it is difficult to form the lead frame and a current conductor in the process of packaging. And then, at the same time, the invention is not suitable for mass production.
(4) Proper shielding has not been sufficiently performed in the case where a flux generated by disturbance or an external interference magnetic field exists around the magnetic field sensor. In other words, it is desirable to guiding a magnetic flux to be measured by a magnetic detection element while suppressing a disturbance flux to be eliminated. If this is done effectively, a current sensor will contain a smaller measurement error and hold enough magnetic shield. In an actual one-chip current sensor, it has not been achieved efficiently yet.
Therefore, the present invention provides a low-cost current sensor suitable for mass production and a manufacturing method, the current sensor is small with high sensitivity and can be packaged in a standard assembly line which is normally used for manufacturing an integrated circuit.
Another object of the present invention is to provide a current sensor which is packaged in a standard assembly line with sufficient shielding effect against a disturbance flux, and to provide a manufacturing method thereof.